Abstract: We propose to continue our i-dropout object survey to search for luminous quasars at z~ 6 using MARS on KPNO 4m. A similar program was granted time during semesters 2003A and 2004A. The observations were very successful, with a total of six new quasars at z=5.8 to 6.2 observed. In 2005A, we will search for quasars from an additonal ~ 1500 deg^2 of multicolor imaging data recently obtained by the Sloan Digital Sky Survey (SDSS). Objects with i-z > 2.2, z<20.4 and blue z-J color will be selected based on optical and near-IR photometry. Follow-up spectroscopy will be obtained using KPNO 4m/MARS, taking full advantage of this red-optimized spectrograph to probe the 8000 - 10000 Aregion. We expect to find 3 - 6 new quasars at 5.7 < z < 6.5 in the new area, increasing the total number of z~6 objects known by \gtrsim 20%. The high-redshift quasar spectra will be used to probe the evolution of the ionizing background and the epoch of reionization. By measuring the Gunn-Peterson effect along different lines of sight, we will study the inhomogeneity of the reionization process. The quasar sample will also be used to study the evolution of the density and the luminosity functions of the quasar population, and to measure the metallicity of high-redshift quasar environments.